It is common practice in the petroleum industry to produce high octane motor fuel by alkylating an isoparaffine with an olefin in the presence of a catalyst which preferably is liquid hydrofluoric acid or hydrogen fluoride (HF). Such a process is commonly knonw as an HF alkylation process or merely an alkylation process. The effluent from the alkylation reactor containing hydrocarbon and acid, is usually passed to a generally vertical arranged settler vessel at an intermediate point along the length of the settler vessel. A hydrocarbon phase is separated from an acid phase in the settler vessel, with the hydrocarbon phase contained in the upper portion of the settler vessel and the acid phase contained in a lower portion of the settler vessel. Accordingly, a liquid-liquid interface between the acid phase and hydrocarbon phase is formed within the settler vessel. As used herein, the liquid-liquid interface is located at a point along the height of the settler vessel where the acid concentration of the material in the settler vessel is greater by a predetermined amount than the acid concentration in the alkylate product supplied to the settler from the reactor. The hydrocarbon phase is fractioned to separate low boiling hydrocarbons from the alkylate product while the acid phase is cooled and recycled to the alkylation reactor for reuse in the alkylation process. As necessary, acid catalyst can be withdrawn from the system for purification. The purified acid catalyst and, as necessary, additional fresh acid is returned to the alkylation reactor.
It is known to improve the economics of an alkylation process by employing two or more alkylation reactors and passing the individual alkylate product streams to a common settler vessel, thereby forming a common pool of acid catalyst in the lower portion of the common settler vessel. Acid catalyst is then withdrawn from the common pool and passed in individual streams to the respective alkylation reactors. While an alkylation system employing multiple reactors and a common acid catalyst pool is effective for reducing equipment cost while maintaining a desired hydrocarbon/catalyst ratio for each reactor, and is also effective for increasing production of high quality gasoline boiling range materials, the system presents certain safety considerations. For example, with a common acid catalyst pool, a leak in one reactor could result in spillage of the entire catalyst pool which supplies the multiple reactors.
Acid catalyst fluid handling systems associated with alkylation processes are designed with due concern for providing a non-leaking catalyst fluid handling system. In order to provide greater safety, however, it is desirable to reduce, as much as possible, the spillage that would occur in the event of a leak affecting the liquid acid catalyst.
Accordingly, it is an object of this invention to improve safety in operating an alkylation process.
A further object of this invention is to increase the safety of a petroleum refining process and the apparatus employed therein.
Another object of this invention is to provide apparatus and method for reducing the spillage of acid catalyst in the invent of a leak in the acid catalyst handling system associated with an alkylation process.